1. Field of the Invention
The present invention relates to an internal EGR control device for an internal combustion engine, for controlling internal EGR which causes burned gases to remain in cylinders.
2. Description of the Related Art
Conventionally, there has been proposed an internal EGR control device of this kind in Japanese Laid-Open Patent Publication (Kokai) No. S62-10411. In this internal EGR control device, the amount of internal EGR caused to remain in cylinders is controlled by changing an intake cam phase and an exhaust cam phase with respect to a crankshaft by a variable intake cam phase mechanism and a variable exhaust cam phase mechanism, respectively, and by changing the lift of an intake valve by a variable intake lift mechanism. Specifically, the opening and closing timing of intake and exhaust valves is controlled by controlling the above-mentioned intake/variable exhaust cam phase mechanism and the variable intake lift mechanism depending on operating conditions of the engine which are determined e.g. according to the rotational speed of the engine and the opening of a throttle valve.
As described above, in the conventional internal EGR control device, the internal EGR amount is controlled only by controlling the opening and closing timing of the intake and exhaust valves depending on the operating conditions of the engine. However, even when the operating conditions of the engine are the same, if conditions of burned gases are different, the internal EGR amount is also different. For example, if temperature or pressure of burned gases is different, the internal EGR amount is also different, and even if the temperature or pressure is same, if the composition of burned gases is different, the internal EGR amount is different accordingly. Therefore, in the conventional internal EGR control device, it is not possible to properly control the internal EGR amount which actually remains in the cylinders, depending on the conditions of burned gases.